The silver salt diffusion transfer process is well known, so that a description of the details of the process is not necessary. Specifically, this process is described in detail in various publications, e.g., A. Rott and E. Weyde: Photographic Silver Halide Diffusion Processes, Focal Press, 1972; J. Sturge, V. Walworth, and A. Shepp: Imaging Processes and Materials: Neblette's Eighth Edition Van Nostrand Reinhold, 1989, Chapter 6: "Instant Photography and Related Reprographic Process"; G. Haist: Modern Photographic Processing, Vol. 2, John Wiley & Sons, 1979, Chapter 8: "Diffusion Transfer"; and so forth.
This diffusion transfer process can be employed with various photographic materials as described in detail in the above-cited texts. In a known method, for example, a photosensitive element having a silver halide emulsion applied on a support is superposed upon an image-receiving element having an image-receiving layer containing silver precipitation nuclei on another support. A processing element which is composed of a highly-viscous alkaline processing composition containing a developing agent and a silver halide solvent is spread between the above two elements.
With the above construction, the photosensitive element is exposed to light, superposed on an image-receiving element, and then a processing element is spread between the above two elements. After a certain time the image-receiving element is removed with a transferred image thereon. Production of transferred images is always desired to be finished more rapidly.
In one method, the finishing of image transfer is accelerated by use of a developing agent having a high reducing power such as a hydroquinone and a silver halide solvent having high dissolving power such as hypo. In this method, however, problems are involved because the transferred images are quite unstable and cannot be preserved for a long term due to staining by an oxidation product of the developing agent and the formation of sulfide caused by a residual hypo. To stabilize the images, an oxidation-preventing layer such as polyvinyl alcohol layer containing an alkalineutralizing agent needs to be formed immediately after the image formation. This complicates the handling of the material.
In another method of acceleration of the finishing of a transferred image, silver chloride, silver chlorobromide, or the like which are highly soluble are used for the silver halide emulsion of the photosensitive element. This method, however, is disadvantageous because the photosensitive element cannot be used for photographing because of its low sensitivity, and because the density of the transferred image is low due to the tendency toward fogging.